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Allegany County Health Department  
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Drinking Water Program

Disinfection Procedure

Water in a recently drilled well is subject to contamination by the drilling operation and from the pipe that delivers the water throughout the house. It is, therefore, necessary to disinfect the well to eliminate bacteria that may have been introduced into the system before the water may be used for drinking purposes. Follow up samples can determine whether or not the contamination of the well is an ongoing concern. Disinfection of old wells is also important when a sample proves positive for bacteria.

A disinfection procedure that may be used is as follows:

  1. Mix ½ gallon of chlorine laundry bleach such as Clorox with ten gallons of water. (For wells with more than 150 feet of water, use one gallon of bleach.)
  2. Pour the 10-½ gallons of solution into the well casing.
  3. Run the water at all of the cold water faucets until the bleach odor is noticeable. It is recommended to wash a load of whites, if possible, in the washer machine.
  4. Once the bleach odor is noticeable at every tap on the system, allow the solution to remain in the pipes for at least 12 hours by not running any water during this period.
  5. After 12 hours, flush the bleach out of the system by running the water until no odor is noticeable. Preferably do not discharge this solution into the septic tank.
  6. The water system should be flushed daily after the disinfection period and a sample can be taken seven days or more after the disinfection.

Consumption of water containing large quantities of bleach is not recommended, caution should be used so that no one drink the water after adding bleach. Prior to requesting a water sample for a new well or before requesting a resample after notification of bacteriological contamination, this disinfection procedure should be performed.

New Wells

This division issues permits for new water supply wells, geothermal wells, and test wells to Maryland licensed well drillers. If you need looking to drill any of the above listed wells, please contact a Maryland Licensed well driller. They will obtain the permit for your Certificate of Potability (COP), which are issued by Environmental Health for all new wells. Environmental Health tests the water for bacterial contamination and certain chemical parameters. , make sure the well has been disinfected either by the well driller or homeowner using the disinfection procedure, before scheduling the samples for a COP. For more information, contact Environmental Health at 301-759-5040.